1. Field of the Invention
The present invention relates to power reduction in vehicle drives for lowering temperature.
2. Description of Related Art
The performance of components of a vehicle drive is essentially a function of the heat output or of the temperature of the particular component of the vehicle drive. Thus, for example an electric drive or an energy storage of an electric vehicle or of a hybrid vehicle has a temperature curve which results in the particular component having to be operated at reduced power if its temperature reaches a maximum temperature at which this component may be damaged. This power reduction, also known as derating, presents no problem, as long it is not performed in driving situations in which the driver expects or needs the full driving power, for example, to carry out, for example, a passing maneuver on the oncoming lane or to merge onto a superhighway. Power reduction is critical, in particular in sporty driving, which makes providing the full driving power necessary.
An excess temperature power regulation is normally used for power reduction with the purpose of avoiding critical component temperatures; when a critical temperature occurs, such regulation forces a brief shutoff of the vehicle or an operation of the vehicle in a state in which the particular component is cooled off, driving being resumed after a cool-off. If the affected component is a generator which supplies an electric motor with electrical power in a power split hybrid vehicle drive train, for example, when a generator excess temperature is reached, the driving power is abruptly reduced, so that the vehicle is drivable at crawling speed at most. For reducing the driving power, a current reduction, such as described in Japanese patent document 11-215888, may be performed.
In fact, there is the possibility of designing the vehicle drive for a maximum sustained driving power for avoiding the power reduction. This requires overdimensioning of the overall system in order to avoid the infrequent special case of excess temperature power regulation, which is associated with high additional costs. Indeed the driver could be pointed, for example, to a component temperature to be reached or to an imminent power reduction via a display. This presupposes that the driver also sees and heeds this display. The disadvantage here is that, if a display of this type is not heeded, one of the components may be damaged by overload, or dangerous driving situations may arise due to an abrupt power reduction.